The mucosa lines various hollow organs and body cavities of the human organism. It serves as a mechanical demarcation and fulfills an important function within the immune system.
What is mucosa?
Mucosa (also tunica mucosa, mucosa) is the protective layer lining the inner walls of hollow organs of the respiratory tract (trachea, bronchi, nose, sinuses), digestive tract (mouth, esophagus, stomach, intestines), urinary tract (bladder, urethra), and reproductive organs (uterus, oviducts, and vas deferens). Oral and nasal mucosa, intestinal and gastric mucosa as well as uterine mucosa and conjunctiva of the eyes belong to the most important mucous membranes of the human organism. As a single- or multi-layered epithelium, the tunica mucosa, unlike the skin, has no hair or horny layer. In addition, mucous membranes either produce and secrete secretions independently or are localized near secretory glands to moisten the tissue. In general, the surface of the mucosa is protected from physical, chemical, or mechanical damage by a mucus layer composed of mucins (glycoproteins) that function as mucins.
Anatomy and structure
The specific structure of the mucosa is adapted to the physiological function of the organs it lines. The mucosa generally consists of an epithelial layer adapted to the particular organ function, called the lamina epithelialis mucosae, a thin muscular layer, the lamina muscularis mucosae, and a loose layer of connective tissue with reticular fibers between them, called the lamina propria mucosae. The epithelial layer can have a single-layered (e.g. in the intestine) or multilayered (e.g. in the oral cavity) structure as well as an enlargement of the surface by microvilli (filamentous protrusions of the cell membrane) and partially also by kinocilia (cilia e.g. in the respiratory ciliated epithelium or in the uterine tuba or fallopian tube) and stereocilia (cell processes e.g. in the deferens duct or vas deferens). The lamina propria of the mucosa often contains glands that moisten the mucosa, although the vaginal mucosa, among others, is an exception and has no glands (cutaneous mucosa). In addition, the lamina propria in the gastrointestinal tract (digestive tract) is embedded in a layer of smooth muscle cells (lamina muscularis mucosae).
Function and Tasks
While the mucosa of the esophagus is responsible for the smooth transport of the food pulp, it also performs a protective function in the nose (against germs) or in the stomach (against gastric acid), and in the gastrointestinal tract it also serves to increase the surface area, which enables better absorption of nutrients. In principle, mucous membranes serve as a mechanical barrier to the surface of the organs they line. In addition, many mucous membranes are able to transport secretions and molecules in a specific direction by means of the transport proteins (including glucose transporters) incorporated into their surface. Accordingly, mucous membranes play an important role within resorption and secretion processes. In addition, mucous membranes can secrete immunoglobulins (antibodies), especially IgA, and through this protective function against invading pathogenic germs, they represent an important component of the microbial immune defense of the human organism. The mucous and serous glands of the bronchial lamina propria produce and secrete bronchial mucus, which moistens the air we breathe. This bronchial mucus causes the moistened cilia of the respiratory ciliated epithelium to move in waves toward the pharynx (approximately 1000 times per minute), so that small molecules (including dust particles and bacteria) attached to this mucus are carried away to the pharynx, where they are swallowed mostly reflexively through the esophagus.
Diseases and complaints
The mucosa exhibits self-protection (also known as mucosal immunity) due to the immunoglobulins secreted independently by the mucosal cells, which depends, among other things, on adequate food intake.Mucosal immunity can be reduced, for example, by environmental stress (pesticides, heavy metals, nicotine, electrosmog), medications, food intolerances, stress, and insufficient sleep. As a result of the reduced self-protection of the mucous membranes, allergic reactions (asthma, hay fever), intestinal colic (cramp-like contractions in the gastrointestinal tract), inflammation of the gastric and intestinal mucosa, viral (rhinitis, bronchitis) and/or bacterial (gastritis or cystitis or inflammation of the gastric mucosa or bladder) diseases can manifest. Stomatitis (inflammation of the oral mucosa) may have infectious (viral, fungal or bacterial), toxic, allergic, physical and/or systemic causes (vitamin deficiency, systemic disease). Prolonged inflammation of the mucous membranes may cause mucosal thickening, which may result in surgical evacuation of the sinus cavity in cases of sinusitis, for example. If the cilia of the respiratory ciliated epithelium of the bronchi are impaired in their function by nicotine abuse or flu-like infections, a cough manifests, which takes over the clearance function of the cilia.
